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Unusual Exposure of Silurian-Devonian Unconformity in Loomis Quarry Near Denver, Lowa

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Unusual Exposure of Silurian-Devonian Unconformity in Loomis Quarry Near Denver, Lowa Proceedings of the Iowa Academy of Science Volume 69 Annual Issue Article 55 1962 Unusual Exposure of Silurian-Devonian Unconformity in Loomis Quarry Near Denver, lowa Fred H. Dorheim Iowa Geological Survey Don L. Kock Iowa Geological Survey Let us know how access to this document benefits ouy Copyright ©1962 Iowa Academy of Science, Inc. Follow this and additional works at: https://scholarworks.uni.edu/pias Recommended Citation Dorheim, Fred H. and Kock, Don L. (1962) "Unusual Exposure of Silurian-Devonian Unconformity in Loomis Quarry Near Denver, lowa," Proceedings of the Iowa Academy of Science, 69(1), 341-350. Available at: https://scholarworks.uni.edu/pias/vol69/iss1/55 This Research is brought to you for free and open access by the Iowa Academy of Science at UNI ScholarWorks. It has been accepted for inclusion in Proceedings of the Iowa Academy of Science by an authorized editor of UNI ScholarWorks. For more information, please contact [email protected]. Dorheim and Kock: Unusual Exposure of Silurian-Devonian Unconformity in Loomis Quar 1962] PHOTOINTERPRETATION 341 Literature Cited Black, R. F. (in manuscript). Ice wedges and pennafrost of the Arctic Coastal Plain of Alaska. U. S. Geo!. Survey Prof. Paper. l Iop1<ins, D. ,\L, and Sigafoos, H. S. (1951). Frost action and wgetation patterns on Seward Peninsula, Alaska. U. S. Geo!. Survey Bull. 974-C. p ..51-100. ·------ (1954). Role of frost thrusting in the fomrntion of tussocks. Am. Jour. Sci., v. 252, p. 55-59. f.:oranda, John J. (unpublished manuscript). The plant ecology of the Franklin Bluffs area, Alaska. Botany Dept., University of Tennessee, Leffingwell, E. deK. (1915). Ground-ice wedges; the dominant form of ground-ice on the north coast of Alaska. Jour. Geology, v. 23, p. 635-6.54. :Vluller, S. W. (1947). Permafrost or permanently frozen ground and related engineering proglems. Ann Arbor, Mich., ]. W. Edwards, Inc., 231 p. !'ewe, Troy L. ( lfl54). Effect of pennafrost on cultivated fields, Fairbanks, Alaska. U. S. Geol. Survey Bull. 989-F. Troll, Carl (1958-translation). Structure soils, solifluction, and frost climate of the earth. U. S. Army Snow, ke & Permafrost Hescarch Establish­ ment, Corps of Engineers, Translation 43. Taber, Stephen ( 1943). Perennially frozen ground in Alaska; its origin and history. Geo!. Soc. America Bull., v. 54, p. 1433-1548. Unusual Exposure of Silurian-Devonian Unconformity in Loomis Quarry Near Denver, lowa 1 FRED H. DoRHEIM2 AND DoN L. KocH2 Abstract. In the Loomis quarry, located in the NW1.4 sec. 29 T. 91N., R. 13W., Bremer County, Iowa, there is an un­ usual exposure of an unconformity between the Silurian and the Devonian sediments. Several Niagaran hummocks rise approximately 30 feet above the general Silurian level with Devonian sediments (Cedar Valley and Wapsipinicon) dcsposited against the Hanks of the Niagaran remnants. A basal Wapsipinicon breccia is exposed in this section. Chert from the Silurian forms an important part of the breccia. INTRODUCTION A most remarkable exposure of an irregular Silurian surface with Devonian sediments deposired along the eroded flanks can be seen in the Charles Loomis quarry located in the NWl/4 sec. 29, T. 91N., R. l3W., Bremer County, Iowa. This quarry is gen­ erally known as the Denver Quarry. The location of the quarry and the routes leading to it from either Waverly or Denver are shown in figure 1. This study was made possible through the cooperation of Beu 1 Presented with the pennission of Dr. H. Garland Hershey, State Geologist, and Director of the Iowa Geological Survey. " Iowa Geologicfl\ Siµyey, Iowa City, Iowa. Published by UNI ScholarWorks, 1962 1 Proceedings of the Iowa Academy of Science, Vol. 69 [1962], No. 1, Art. 55 342 row A ACADEMY OF SCIENCE [Vol. 69 R 14 W R 13 W z a; N ,_ c--·· I I I I I I 0 2 miles~--~-~ FIG. I - LOCATION MAP OF DENVER QUARRY and Sons Limestone Company, who opened and operated the quarry, and of the owner, Mr. Charles Loomis. The work was done as a part of Iowa Geological Survey official activities. As­ sociates at the Iowa Geological Survey have made helpful sug­ gestions. Dr. Brian F. Glenister, State University of Iowa, helped in the identification of fossils. DISCUSSION General The locations of the various features to be discussed are shown in figure 2. Of special note is the Niagaran hummock about mid­ way on the west wall flanked on the north by sediments of the \Vapsipinicon Formation. Hummock, as used here, refers to elevations above the general Silurian top, either as conspicuous rises or as lesser undulations. Two Niagaran hummocks occur in the east face of the quarry with Devonian sediments deposited adjacent to each of them. A fourth hummock is exposed in the stripped area northeast of the quarry. Here an area of 0.1 acre of Niagaran rock can be seen surrounded by Devonian sedi­ ments. Stratigraphy and Lithology The following stratigraphic section was measured along the north wall of the quarry (fig. 2). The bed numbers used in this section are the same as those used on the graphic section (fig. 3). https://scholarworks.uni.edu/pias/vol69/iss1/55 2 Dorheim and Kock: Unusual Exposure of Silurian-Devonian Unconformity in Loomis Quar 1962] SILURIAN-DEVONIAN CONFORMITY 343 Location at which basic jii;ipped­ stratigraphic section Nlagaran hummock expased Area was measured I r­ as Isolated mound; about .1 I { I 0.1 acre 1... __ ) Cedar Valley and Cedar Valley and Wapsipinicon over adjacent to Niagaran on north side of hummock Niagaran hummocks Wapsipinicon on south side of hummock Saddle-Wapsipinicon over th inning Niagaran---' Large Niagaran / hummock~ Scale (feel) 50 100 200 Fig. 2 - Map of Denver Quarry, showing location of Niagaran hummocks. Stratigraphic Section as Observed Along North Wall of Quarry Bed Description Thickness Pleistocene Loess and till ....... about 12' Devonian System Cedar Valley Formation. 1. Limestone, grayish-orange (IOYR7 /4) to very pale orange ( 10YR8/2), medium elastic, with numerous brachiopod frag­ ments and a few crinoidal stem sections. Badly weathered reticulate atrypoid brachiopods are locally abundant in lower part of bed. Dendrites of manganese oxides occur throughout. The heels are platy and badly slumped with geest distributed throughout ............... 10' max. 2. Breccia composed of fragments of grayish-orange ( 10YR7 I 4) calcareous dolomite, soft and friable, in a matrix of calcareous shale. Most of the fossils are very poorly preserved. Among those collected are Productella, Schizophoria meeki Fenton & Fenton, Atrypa devoniana Webster, and A. lineata Stain­ brook. Manganese oxides occur as scattered specks along with glauconite in the upper part of this bed and are abundant in the lower part . 15' \Vapsipinicon Formation .3. Limestone, very pale yellowish-brown ( 10YR7 /2) to yellow­ ish-gray ( 5Y7 /2), lithographic to very fine crystalline, lamin- ated to brecciated with large solution cavities (fig. 8-A) and some flutings. The breccia is composed of small blocks of lithographic limestone in a limestone matrix. Bedding is irregular . .. .. .. .. .. .. .. .. .. .. .. .. .. .. lY Published by UNI ScholarWorks, 1962 3 Proceedings of the Iowa Academy of Science, Vol. 69 [1962], No. 1, Art. 55 .344 10\VA ACADEMY OF SCIENCE [Vol. 69 .. >­a:: c <( ~ z s a:: :ii ~ a.. 0 LEGEND l.imestcne dolomitic Dolomite aroillaceous argillaceous, and sandy cherty Shale -- brachiopods EB crlnolds e> corals ~z <( ~ "O Vertical Scale (feel) c a:: 0 ::::> ..)( ....I <( Cf) Fig. 3- Stratigraphic section as exposed in north face of quarry and in sump along west face. 4. Limestone, as in bed .3 but more massive and with irregular solution cavities . 6-8' 5. Dolomite, pale yellowish-orange ( 10YR8/6), soft structure­ less, friable. Thirty percent of an insoluble residue sample consisted of clay and silt. A thin layer of dark-brown to orange to gray clay, silt, and sand caps the dolomite. \Vhen treated with acid about .30 percent of a sample from this layer digest­ ed. The remaining 70 percent was two-thirds clay and one- third quartz silt. Total thickness of bed 5 varies from . .3J~-5' 6. Limestone,_ vari-colorecl, mostly yellowish-gray ( 5Y7 /2), very dolomitic, very argillaceous; with a few grains of rounded quartz sand and angular grains of dark gray chert sand. Less than 10 percent of the sample is composed of very sharp chips https://scholarworks.uni.edu/pias/vol69/iss1/55 4 Dorheim and Kock: Unusual Exposure of Silurian-Devonian Unconformity in Loomis Quar 1962] SILURIAN-DEVONIAN CONFORMITY 345 of white ( N9) chert. Thc,e whit« chert l'hip; were derived ~1 from the Silurian . 1.. ) 7. Limesotne hrecda (fi,g. 8-B), grayish-yellow (5Y8/4) to Vl'ff pale orange ( 10YH8/2 ), Vt•ry coarse, fragmental; with n fo~,. sane! grains, angular gray chert, and larg'' angular d1ips of ~1 white chert I ' ,') Silurian System Alexandrian Series 8. Dolomite, grayish-orange ( 10YR7 / 4) to yellowish-gray ( 5Y- 7.12), medium-fine, ha rel; with crystalline· calcite and chert nodules. The chert is medium-gray ( i\-6) to yellowish-gray ( .5Y7 /2) in the center of tlw nodule but wc,1tlwrs white on the surface. Silkifiecl Stromatopora and corals common 18' Soutr. North o' 200' 300' Fig. 4-Diogrom of west wall of quarry showing large Silurian hummock with Devonian beds deposited on and adjacent to the eroded surface It is significant that neither the Niagaran nor the upper 8 feet of the Alexandrian is represented in this section. The Silurian rises most conspicuously above the quarry floor in the large hummock on the west side (figs. 4 and 6), nearly to the level of the top of bed 2 (fig. 3), the middle of the Cedar Valley, as exposed in the quarry. At this point there is approxi­ mately 2.5 feet of Niagaran underlain by about 8 feet of inter­ bedded chert and dolomitic limestone of the Alexandrian.
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